1. Field of the Invention
The present invention relates to a primer composition which promotes adhesion between a polyurethane-based adhesive or sealant and a substrate.
2. Description of the Related Art
Organo-silicon and organo-titanium coupling agents have been used as adhesion promoters, either mixed directly in a sealant/adhesive formulation or in a primer composition for surface pretreatment prior to application of the sealant/adhesive onto substrate surfaces. Due to their high reactivity and high cost, these coupling agents are generally not suitable for use at high concentrations in sealant/adhesive formulations. On the other hand, for many applications, no significant improvement in adhesion properties of the sealant/adhesive is obtained when only small amounts of the coupling agent are added to the sealant/adhesive composition.
Thus, incorporation of organo-silicon and organo-titanium coupling agents into primer compositions may be a more practical use of those coupling agents. Although the use of primers introduces an additional step in the application of the sealant/adhesive to a substrate, application of primers remains popular due to their powerful adhesion-promoting effect.
Conventional primer compositions based on organo-silicon and/or organo-titanium coupling compounds generally contain a large amount of volatile organic solvents. The organic solvents play a role not only in adjusting the viscosity of the primer composition, but also as stabilizers thereby providing a longer shelf-life of the primer composition.
The solvents used in the formulation of conventional primer compositions are typically volatile organic compounds (VOC). While such compositions provide good adhesion enhancement properties, the release of VOC during the fabrication, storage or use of the primer composition can cause significant harm to the environment. The environmental concerns associated with the use of VOC has prompted the promulgation of government regulations requiring that the use of these compounds be drastically reduced and ultimately eliminated. In view of the regulations against VOC emissions, there has been an increasing effort to develop low VOC and VOC free primer compositions.
The present invention relates to an aqueous primer composition which promotes adhesion of polyurethane adhesives or sealants to a substrate. The primer composition of the invention is stable and gives little or no VOC emissions.
It is an object of the present invention to provide an aqueous primer composition which promotes adhesion of polyurethane adhesives or sealants to a substrate. Preferably, the primer composition is stable and gives little or no VOC emissions.
In one aspect, the invention provides a method of adhering a polyurethane-based sealant or adhesive to a substrate, comprising:
i) applying an aqueous primer solution onto a substrate, the primer solution comprising water and an aminotitanate compound,;
ii) applying a polyurethane adhesive or sealant to the primer-treated substrate; and
iii) forming a reaction product of the primer and the polyurethane.
In another aspect, the invention provides a substrate having thereon a layer of a polyurethane adhesive or sealant, comprising:
i) a substrate;
ii) a layer of a polyurethane adhesive or sealant; and
iii) a primer between the substrate and polyurethane adhesive or sealant, said primer comprising an aminotitanate compound;
wherein the primer and polyurethane have formed a reaction product.
It is another object of the present invention to provide an aqueous silane-based primer composition which promotes adhesion of polyurethane adhesives or sealants to a substrate. Preferably, the primer composition is stable and gives little or no VOC emissions.
In one aspect, the invention provides a method of adhering a polyurethane-based sealant or adhesive to a substrate, comprising:
i) applying an aqueous primer solution onto a substrate, the primer solution comprising water, an aminotitanate compound, and an epoxysilane compound having at least one epoxy group and at least two alkoxy groups;
ii) applying a polyurethane adhesive or sealant to the primer-treated substrate;
iii) forming a reaction product of the primer and the polyurethane.
In yet another aspect, the invention provides a substrate having thereon a layer of a polyurethane adhesive or sealant, comprising:
i) a substrate;
ii) a layer of a polyurethane adhesive or sealant; and
iii) a primer between the substrate and polyurethane adhesive or sealant, said primer comprising an aminotitanate compound and a siloxane formed from condensation of at least one epoxysilane compound having at least one epoxy group and at least two alkoxy groups;
wherein said the primer and the polyurethane have formed a reaction product.
In still another aspect, the invention provides an aqueous primer solution comprising an epoxysilane compound having at least one epoxy functional group and at least two alkoxy groups, an aminotitanate compound and water, wherein the epoxy group is hydrolyzable to an ethylene glycol functionality and the aminotitanate compound improves adhesion of a polyurethane adhesive or sealant to a substrate relative to said primer not containing said aminotitanate compound.